Recording and reproducing devices for compact cassettes (hereinafter referred to as C-cassettes) have been widely used. The C-cassettes hold a magnetic tape on/from which audio analog signals are recorded/reproduced. In consideration of the C-cassette format, tape material and the analog recording system, however, a further improvement in the quality of reproduced sound is not expected.
To improve sound quality, in recent years, a recording and reproducing device, namely R-DAT (Rotary Head Digital Audio Tape Recorder) is developed. The R-DAT performs recording and reproduction by a helical lead system in which audio signals are converted into digital signals, and recorded and reproduced by a rotary head.
The R-DAT records and reproduces digital signals and performs various error corrections. Therefore, the R-DAT gives a more accurate or less distorted reproduction of the original sound in comparison to the sound reproduced by C-cassette recording and reproducing devices. In other words, the quality of sound reproduced by the R-DAT is much better than that reproduced by the C-cassette recording and reproducing devices.
However, in spite of improved sound quality, the R-DAT is not so widely used due to the following reasons.
One of the reasons is that the R-DAT system is designed without considering compatibility with the conventional widely spread C-cassette format. It is therefore difficult to produce R-DATs compatible with C-cassettes. Another reason is high prices of cassettes holding a magnetic tape for R-DAT.
Recently, there has been a proposal to develop a recording and reproducing device which digitally records or reproduces information on a magnetic tape contained in a cassette whose dimensions are substantially equal to those of C-cassettes. A recording and reproducing device capable of operating with the digital cassette (hereinafter referred to as D-cassette) is easily made compatible with both the D-cassettes and the C-cassettes.
In addition, although the D-cassettes have dimensions similar to those of the C-cassettes, various measures are taken to improve the running of a magnetic tape in the D-cassettes, thereby enabling faithful digital recording and reproduction.
The following description discusses the dimensions of the C-cassette and the D-cassette. Both of them are substantially rectangular parallelepiped containers. The length and the width of the C-cassette are equal to those of a D-cassette. The D-cassette has a thickness which is 0.9 mm greater than that of the C-cassette. The term "cassette" is simply used hereinafter in a statement referring both the D-cassette and the C-cassette,.
As shown in FIG. 17, an opening 41"c is formed in the base of a C-cassette 41". Recording and reproduction are performed by inserting into the opening 41"c a magnetic recording and reproducing head (not shown) and feeding a magnetic tape 40 held in the C-cassette 41" past the head.
In contrast, as shown in FIG. 18, a D-cassette 41' does not have raised sections which are formed on the front and back sides of the C-cassette 41". The D-cassette, however, includes indents 41'd which cooperate with guide elements of a cassette holder. The D-cassette 41' has reel holes 41'e formed in one side as illustrated in FIGS. 18 and 20. Since the reel holes at 41'e do not go through the other side, the D-cassette 41' is placed on a reel set of a recording and reproducing device only in a predetermined direction.
Next, the following description discusses a significant difference between the C-cassette 41" and the D-cassette 41', namely the slider of the D-cassette 41'.
As shown in FIG. 19, a slider 41'a made of a metallic sheet for covering the opening 41'c from which a head is inserted is mounted to be movable in the longitudinal direction of the D-cassette 41'. The slider 41'a is always pushed by a spring, not shown, to cover the opening 41'c. To expose the opening 41'c by pushing the slider 41'a, the D-cassette 41' is provided with a hole 41'b. The hole 41'b is formed in a position adjacent to an edge of the slider 41'a closed. FIG. 18 shows a state in which the slider 41'a covers the opening 41'c, while FIG. 19 shows a state in which the opening 41'c is not covered with the slider 41'a.
Meanwhile, the C-cassette 41" is not provided with a slider and therefore the magnetic tape 40 is exposed at the opening 41"c as shown in FIG. 17. The slider structure of the D-cassette 41' protects the magnetic tape from dust and electromagnetic waves.
A recording and reproducing device for use with the D-cassette 41' is described below. The recording and reproducing device has a cassette holder for carrying the D-cassette 41' between the discharge position and the record-reproduction position. It has been proposed to incorporate into such a device a mechanism for moving the slider 41'a to cover and uncover the opening 41c at the record-reproduction position by the driving force of the driving means such as a motor.
With this mechanism, however, the slider 41'a is opened after the cassette holder reaches the record-reproduction position, resulting in a longer operation time. Moreover, since the mechanism has a complicated structure, it requires a long time to control the mechanism and is difficult to manufacture a compact recording and reproducing device.
To avoid such problems, a slider moving mechanism was proposed. With this mechanism, when the D-cassette 41' is manually placed in the cassette holder, the slider 41'a is opened with the use of the force of the hand to push the D-cassette 41' into the cassette holder. In this mechanism, a rotating lever is installed on the cassette holder to open or close the slider 41'a. A slider pin for moving the slider 41'a is mounted on the free end of the lever so that the slider pin protrudes into the cassette holder. And the hole 41'b of the D-cassette 41' is formed so that the slider pin of the slider 41'a comes into contact with the hole 41'b.
With this mechanism, when the D-cassette 41' is placed in the cassette holder, the slider pin fits into the hole 41'b. When the D-cassette 41' is pushed further into the cassette holder, the lever is rotated, for example, counterclockwise and the slider pin pushes and opens the slider 41'a.
Similarly, when the C-cassette 41" is inserted into the cassette holder, the lever is rotated. However, the slider pin is installed so as not to interfere with the insertion of the magnetic head into the opening 41'c of the C-cassette 41".
The lever is pushed toward a direction in which the cassette is pushed out of the cassette holder, and pushes the cassette out of the cassette holder by a predetermined amount when discharging the cassette from the cassette holder. On the other hand, when inserting the cassette into the cassette holder, the lever is rotated against the pushing force by the use the force of the hand.
In the above-mentioned mechanism, in order to move the slider 41'a by a predetermined distance, the distance between the axis of rotation of the lever and the slider pin must be slightly longer than the predetermined distance. Furthermore, in order to reduce the size of the cassette holder and of the recording and reproducing device, it is necessary to locate the slider pin so that the straight line connecting the slider pin in the stand-by position where it is out of contact with the cassette and the above-mentioned axis of rotation is almost parallel to the cassette inserting direction.
However, when the above-mentioned straight line is almost parallel to the cassette inserting direction, the angular moment for rotating the lever is small at the beginning of inserting the cassette.
Therefore, in the above-mentioned mechanism, to rotate the lever against the force pushing the cassette out of the cassette holder, increased power is required in inserting the cassette.